Rail base



FIG. 1 is a perspective view of a rail base.

FIG. 2 is a top view of the FIG. 1 rail base.

FIG. 3 is a bottom view of the FIG. 1 rail base; and,

FIG. 4 is a side view of the FIG. 1 rail base.

The broken lines in the drawing depict portions of the rail base that form no part of the claimed design. 

CLAIM I claim the ornamental design for a rail base, as shown and described. 